In my copending application Ser. No. 765,077, filed Feb. 3, 1977, I have described an electromagnetic sound generator with a generally cylindrical housing in which a disk-shaped membrane or diaphragm of ferromagnetic material, peripherally clamped between two housing parts, carries an armature of an electromagnetic coil confronting a stationary core member across an axial air gap. The stiffness of that diaphragm creates a restraining force which maintains the air gap in the de-energized state of the coil and limits the amplitude of the vibrations excited in response to an applied alternating field. Thus, the sound waves generated by the device are affected by the width of this air gap which, accordingly, should be properly calibrated.
In an electropneumatic sound generator, the diaphragm generally blocks an air channel in its quiescent state by contacting a tubular boss at an entrance end of that air channel from which it is intermittently lifted by an air flow entering the housing. Here, again, the resiliency of the diaphragm--which may be supplemented by the thrust of a pressure member supported on the housing--creates a restraining force which opposes the axial separation of the two components and thus determines the response to the sound generator to an actuation of the operating means, i.e. to the activation of a source of air pressure in this instance. A proper calibration of the contact pressure is particularly important where air from the same source is fed simultaneously and in parallel to two or more sound generators of this type to generate different musical notes; if the restraining force in one of these sound generators is significantly lower than in another, the latter will be largely bypassed by the air flow which follows the path of least resistance.
Even if a sound generator of either of the above-discussed types is properly adjusted at the time of assembly, the setting of its rather delicate parts may be disturbed during subsequent handling. Conventional readjusting means solve this problem only imperfectly.